dell-wmi: Don't report keypresses for radio state changes

The WMI events associated to KEY_WLAN are for all the radio devices
available. Use KEY_RFKILL instead since it's more appropriate.

The state of radio devices is changed directly by the BIOS when hotkeys
are pressed, so no events should be reported.

Signed-off-by: Gabriele Mazzotta <gabriele.mzt@gmail.com>
Merged two patches modifying this one line
Signed-off-by: Darren Hart <dvhart@linux.intel.com>